1. Field of the Invention
The invention pertains to mercury vapor discharge lamps. More particularly to a target on the quartz envelope surface that faces the electrical discharge within the lamp, that forms an amalgam from the mercury vapor within the envelope.
2. Description of the Prior Art
In many mercury vapor lamps in use, a small bead of indium is fused onto a micron thin layer of gold coating on the inside surface of the quartz envelope of the low pressure mercury vapor discharge lamp. The indium later forms an amalgam with the mercury vapor in the lamp for vapor concentration control purpose.
U.S. Pat. No. 3,263,111 patented Jul. 26, 1966 by U.W. Doering describes adding an amalgam body consisting of mercury plus gold, silver, tin or potassium to the inner wall of a flourescent tube to control the level of mercury vapor pressure within the tube. U.S. Pat. No. 3,263,111 is hereby incorporated by reference.
U.S. Pat. No. 4,020,378 patented Apr. 26, 1977 by Morehead describes a bit made of indium and tin pressed against the glass stem within the tube while the glass is heated and the bit fuses to the glass. Larger bits are held in place by an overlying porous layer of inert material.
It is one object of the invention to fuse indium to the surface of the quartz envelope of a mercury vapor lamp.
It is another object of the invention to fuse an indium and titanium mixture to the surface of the quartz envelope of a mercury vapor lamp.
It is another object of the invention to provide an indium and titanium target fused on the inside surface of the quartz envelope of a mercury vapor lamp for formation of an amalgam from mercury that is added to the tube.
A low pressure mercury vapor discharge lamp includes a hermetically sealed envelope. The wall of the envelope includes an elongated quartz tubular portion. At least one thermionic electrode, mercury vapor, and at least one inert gas are in the envelope. A mixture comprising indium metal and titanium metal fused together and to the inside of the quartz tubular portion is spaced from the electrode toward the center of the tubular portion, and is exposed to the mercury vapor.
A method for making a low pressure mercury vapor discharge lamp includes the steps of inserting a thermionic electrode in a first end of a quartz tube that is transparent to radiation products of low pressure mercury vapor discharge, hermetically sealing the first end of the tube around electrical leads from the electrode, placing a measured amount of indium metal combined with titanium metal on the inside surface of the quartz tube, applying heat to the quartz until the indium and titanium are melted and fuse to the quartz tube, and inserting mercury into the tube.